Taking advantage of the UAV’s ability to fly freely in the three-dimensional (3D) space , the RIS can be mounted on the UAV. This allows the RIS to fly along with the UAV, which is more flexible in adjusting its 3D location than the conventional terrestrial RIS, thus enhancing communication services [1]}, [2]}. Specifically, an aerial RIS was deployed in [3]} to expand the coverage of communication services, where the worst-case signal-to-noise ratio (SNR) was improved by jointly optimizing the transmit beamforming, the RIS's placement, and the 3D passive beamforming. In [4]}, multiple users were served by a base station (BS), and their received powers were significantly enhanced with the aid of an aerial RIS. To provide communication services for blocked users that locate far apart while preventing information leakage, the UAV equipped with one RIS was deployed in [5]} to improve the security and energy efficiency. However, above works only took the simplified LoS channel (LC) into account, which has two limitations. \(i)\)  The LC model cannot fully capture the critical effects of the UAV location-dependent path loss and shadowing in urban areas with typically high and
dense buildings/trees[6]}; \(ii)\)  The LC model cannot accurately describe the elevation angle-distance trade-off, since the elevation angles between the UAV and ground nodes (GNs) are closely related to the UAV trajectory. Therefore, if the UAV trajectory designed under the LC model is applied in practical urban environments, it will undoubtedly cause significant performance loss. [7]}.
